Introduction 

During the summer of 1905 many of the trees in the Wau- 
sau trial orchard were found to be suffering from some disease. 

In the ease of many of the Northwestern Greening trees the 
foliage on one or more of the larger branches appeared dwarfed 
and wrinkled and later turned brown but did not fall. 

On examination it was found that these branches were gird- 
led at the base or point of union with the trunk. The bark in 
the crotches was brown and sunken, the injury extending 
through the cambium to the sap wood. 

Further investigation in the orchard showed hundreds of 
trees to be affected, some like the Northwestern in the crotches, 
others having large patches of dead bark on the trunks. 

It was not until the close of the growing season that it was 
definitely determined that the trouble was caused by the apple 
tree blight canker. It has since been found that the disease is 
widely prevalent in the state, having been found in twenty-six 
counties and probably exists in the majority of young orchards 
throughout the state, attacking the crotches and trunks of 
young apple trees. 

The apple tree blight canker and methods of treatment were 
fully described by II. EL Whet/el, plant pathologist. Cornell 
University, at the 1906 annual meeting of this Society and the 
address printed in the 1906 Annual Report. 

That a better knowledge of the disease and the means of com- 
bating it may be had the article is here reprinted. 

F. Cranefield, Secretary. 




Fig. 1 — Typical blight canker on 
main limb of young tree. 



Fig. 2— Typical canker showing 
the crack about the margin where 
the diseased bark has dried away 
from the healthy tissue. 



Note — Figs. 1 to 13 inclusive from Bulletin 236, Cornell University, 
Ithaca, N. Y. Figs. 14, 15, 16 and 17 from photographs of trees in the 
Wausau Trial Orchard. 



The Blight Canker of Apple Trees 

H. II. WHETZEL. 

During recent years several kinds of cankers occurring espe- 
cially upon apple and pear trees have been described and fig- 
ured in bulletins from different experiment stations in this 
country. By careful inoculation experiments these various 
cankers have been shown to be due to different species of either 
fungi cr bacteria. Growers very generally even at the present 
time attribute such injuries to "sun scald"' or "freezing." 
Lack of knowledge cf the nature of fungous and bacterial 
growths, together with the ease with which responsibility may 
be shifted upon the weather, lias made this opinion the common 
and natural one. Not only have experiment station workers 
shown that these injuries are usually due to the attacks of liv- 
ing organisms rather than to the results of weather conditions, 
but they have demonstrated that the different forms ef these 
cankers are due to distinctly different organisms. 

The term "canker" then has come to be a very general one 
and is applied to diseases which cause the death of definite 
areas of bark en the limbs and bodies of trees. At least six 
distinct canker diseases of apple and pear tins have been de- 
scribed and figured in recent years. Each ef these cankers have 
been proven to be due to distinctly different kinds of fungi. 
In this paper, however, we shall deal with a canker disease, not 
caused by a fungus and differing strikingly from those already 
mentioned. To this disease I have given the name of blight 
canker. 

THE DISTINGUISHING CHARACTERS AND APPF.ARAXCE OP THE 
CANKER. 

The blight canker while it may occur on trees of almost any 
age is most destructive on young trees just coming into bearing, 
trees from 8 to 15 years old. Old trees weakened by age and 



6 



Wisconsin State Horticultural Society 



neglect may suffer seriously from its attacks and the dead limbs 
protruding here and there from the green foliage in old or- 
chards are often to be attributed to the ravages of this canker. 
In young trees with smooth bark the cankers are easily de- 
tected even in their first stages. They appear as discolored and 





Fig. 4 — Typical pit cankers in the body of 
a tree from which the diseased bark has 
dropped out. The upper one is exuding 
sap, — " bleeding." 

Fig. 3 — Cankers in body of tree resulting from the renewal of activity sea- 
son after season. Observe that these started from small pit cankers which 
partially healed each season. The disease the following season destroyed all 
the bark growth, leaving only the little bit of wood formed in the callus. 
This still persists. 

somewhat shrunken areas, the margin along the advancing front 
being usually slightly raised or blistered. The tissue in ac- 
tively spreading cankers is of a darker green than the healthy 
bark and is very watery or sappy. On damp cloudy days drops 
of a milky, sticky fluid exude from the cankered tissues through 



The Blight Canker of . Xpple Trees 7 

the lenticles or pores in the bark. After a short time the dis- 
eased tissue begins to turn brown and dry out. Unless in a 
very active slate of progress the margins are quite distinct, 
marked by a crack where, in drying, the diseased tissue has sep- 
arated from the healthy bark. The older cankers are brown 
somewhat darker than the healthy bark. They are distinctly 
sunken. The surface is smooth, never checked or roughened or 
beset with pustules or pimples, except in the old cankers where 
after a time rot fungi gain entrance and thriving in the already 
dead tissue produce their fruit bodies on the surface. The prog- 
ress of the spreading canker depends largely upon the continua- 
tion of favorable weather conditions, which seems to he a humid 
atmosphere and cloudy days. With the return of bright, sunny 
weather the active spread of the canker is cheeked abruptly, 
cften to be resumed again with the return of favorable condi- 
tions. This checking and renewing of activity sometimes re- 
sults in large cankers with concentrically arranged cracks within 
the cankered area. This renewal of activity may take place 
during the same season or the canker may partially heal over 
to spread anew the following year. A large per cent of the 
cankers are active during but one season. There are always 
some, however, in which the disease is perennial, living through 
the winter to become active again the following spring, spread- 
ing and enlarging the original limits of the cankered area. 
These "hold over" cankers, as they are called, are the danger- 
ous rues. They are the source of infection for the following- 
year. The diseased bark is usually killed to the wood, to 
which it clings tenaceously the first season. It gradually de- 
cays, however, and falls out, leaving the wood hare and exposed. 
In small cankers, the cone of diseased bark may he quickly 
forced out by the rapidly forming calluses which heal and close 
the canker wound. In some cases the canker is superficial, 
never reaching the cambium except perhaps in a limited area 
at the point of infection. Such wounds heal quickly beneath 
the dead bark which clings to the tree as a sort of scab. 

The cankers vary in size from half an inch in diameter to as 
much as a foot or more in length and several inches across. On 



Wisconsin State Horticultural Society 



healthy, vigorous trees they are small and more or less circular 
in outline. They form funnel-shaped wounds with the small 
end at the cambium. These I have designated as "pit cankers." 
Often the dead bark remains as a sort of lid to the pit but it is 
easily removed with the finger or a knife blade. I have seen 
young trees with limbs and bodies literally covered with these 









1 


I 


* 




i ijH^RI , ,; 












Fig. 5 — Large body canker result- 
ing from successive seasonal attacks 
of the disease. Originated at the 
pruned stub. 



Pig. 6 — Large body canker near base 
of tree, often referred to as "collar rot." 
The tree has made repeated attempts to 
heal this wound, 



The Blight Canker of Apple Trees 9 

pit cankers in all stages of healing over. Aside from affording 
an entrance to rot fungi such cankers unless they enlarge do 
not seem to seriously affect the health of the tree. In many 
cases these pit cankers do not heal properly or at all and the 
disease spreading the same or the following season forms the 
large and dangerous 'limb" or "body cankers." 

"Crotch cankers" usually appear in the crotches where the 
main limbs arise from the body but may also appear in the sec- 
ondary crotches well up in the tree. In general characters they 
are similar to the limb and body cankers. Owing to their pe- 
culiar position water is retained more readily in the dead bark, 
thus affording the very best of conditions for the entrance and 
growth ( f rot fungi. These find easier access to the heart wood 
at the crotch than on the limbs. It was observed that these 
crotch cankers heal much less readily and successfully than do 
the limb and body cankers. Crotch cankers unless promptly 
attended to means the almost certain destruction of the trees. 

The large cankers at the bases of young trees frequently re- 
ferred to by growers as "collar rot" are in many cases very 
probably due to the same cause as that of the cankers on the 
upper parts of the tree. 

HOW THE DISEASE AFFECTS THE TREE. 

The effect of the blight canker upon the tree is to lower its 
vitality to a greater or less degree by cutting off the food sup- 
ply to the roots and thus indirectly reducing the flow of sap to 
the branches and leaves. In other words, it acts the same as 
"girdling." The "collar rot" and "crotch cankers" seem to 
be the most fatal to the tree. The effects of the canker are 
first evidenced in the foliage. If there is a large body canker 
the entire tree may show the effects of the trouble. More often 
the first symptom noted by the grower is the peculiar appear- 
ance of the foliage on one or more of the limbs. Kit her these 
branches fail to leaf out at all in the spring, or if they do the 
leaves never fully expand but remain undersized and curled or 
inrolled. Thev never take on the dark green color of healthy 



10 



/ / Hsconsin State ^Horticultural Society 



foliage, remaining pale and gray. Growers often refer to such 
trees as having "mouse ear" leaves. As the season advances 
and the cankers spread, the leaves often die and dry up on the 




FlG. 7— Canker on pear tree resulting 
from inoculation with bacteria from 
active canker on apple tree. 



Fig. 8 — Pruned stub canker 
that has spread down side of 
limb during early spring of 
second year. Diseased tissue 
cleaned away, trsated with 
corrosive sublimate and 
painted. Good calluses 
formed. Canker ceased to 
spread. 



The Blight Canker of Apple Trees 1 1 

branches. Sometimes badly affected trees will pull through un- 
til autumn or even live for two or three seasons. Such trees 
have scanty foliage, blossom profusely and frequently set a 
heavy crop of fruit. This fruit falls prematurely or is small 
and inferior in quality. 

Such affected limbs and trees, as if in anticipation of their ap- 
proaching death, seem to devote their expiring energy to one 




Fig. 9 — Canker on limbs of apple which originated 
through blighted spurs. 

grand ami final effort to reproduce themselves. As already 
stated, where the trees are strong and vigorous they frequently 
succeed in promptly healing the canker wounds. The dead 
bark of the canker makes, however, an excellent infection court 
for the entrance into the tree of "heart rot" and other decay 
inducing fungi. Moisture so necessary to the germination and 
growth of the spores of fungi, is retained for a considerable 
time in the dead tissue. This is more especially true of crotch 
cankers. No doubt these rot fungi are often to blame for the 
final death of the tree. The heart wood of badly affected limits 
and trees is commonly found to be soft and rotten with only a 
thin rim of sound sap wood surrounding it. 



12 



Wisconsin State Horticultural Society 



THE CAUSE OF THE CANKER. 

A microscopic examination of the viscid milky drops that ex- 
ude from freshly cankered surfaces on moist, cloudy days will 
show them to be composed almost entirely of minute rod-shaped 
bacteria. The diseased tissue within the bark will also be found 
to be alive with these minute plants. By their rapid growth 
and multiplication within the cells of the bark they cause its 




Fig. 10 — Recently blighted shoot on limb of Greening 
apple tree with well marked active canker about its base. 

death. They are not carried along in the sap but slowly work 
their way from cell to cell. When the canker dries down they 
die and disappear so that examination of the tissue of old 
cankers does not show them. That they are the direct cause of 
the disease was proven in the following manner : Bacteria 
from the cankered tissue was introduced into the bark on the 
body of a healthy apple tree and also into the bark of a healthy 



'The Blight Canker of Apple Trees 



13 



pear tree, with the result that typical cankers appeared in botli 
cases. Blossoms and growing twigs of both pears and apples 
were also inoculated with bacteria from this same canker. These 
nearly all developed good cases of blight in about ten days, 
while twigs and blossoms punctured with a sterile needle gave 
no infection. This last experiment was twice repeated during 




Fig. 11 — Pruned stub canker. In- 
fected at time of pruning, probably 
by the saw. Note the color of dead 
bark. 



PlG. 1- — Canker formed about the 
mouth of the burrow of a borer near 
base of an apple tree. 



the summer with pure cultures of the bacteria from the apple 
tree canker. The blighl resulted in practically every case. 
young fruits of both the pear and apple were also Inoculated 
and gave well developed cases of the disease. By a compara- 
tive study in various culture media of the bacteria from cank- 
ers, twigs and fruits of both pear and apple obtained from dif- 
ferent orchards about [thaca the organism of the canker was 
shown to be identical with that of the well-known "lire blight" 
of Ihe pear and "twig blight" of the apple, Bacillus amylov- 
orous. 



1 4 Wisconsin State Horticultural Society 

HOW TREES BECOME INFECTED. 

Only those ways of infection which personal observation has 
discovered are here recorded. No doubt the bacteria enter the 
bark in still other ways than those I have observed. 

Early in my investigation I came to the conclusion that the 
bacteria frequently get into the bark of the limbs and body by 
way of short spurs and watersprouts. The opinion was fully 
confirmed later in the season. Twig blight became very preva- 
lent during July and August, especially in the region about 
Ithaca, X. Y. It was then an easy matter to find blighted spurs 
and watersprouts with active cankers about their bases. Where 
these watersprouts grew out from the trunks as is often the 
ease in young trees, typical body cankers were formed. The 
in lection of the sprout itself is generally attributed to the work 
of insects which after visiting freshly cankered spots or blighted 
twigs introduce the bacteria into tin 1 succulent tissues of the 
rapidly growing healthy shoots. The blighted watersprout socn 
dries up and falls away, leaving often a very indefinite scar in 
the cankered area so that the following season it is usually im- 
possible to tell with certainty the manner cf infection. Obser- 
vation of a large number of trees, during the past season, con- 
vinces me that the blighting of adventitious shoots on trunk 
and limbs is responsible for a majority of the cankers in such 
l< cations. A number of cankers were produced in this w r ay by 
artificial inoculation. 

Another source of infection was found to be the pruning 
knife. Along one side of an orchard of some 350 trees which 
was under observation throughout the season, it was early no- 
ticed Hurt the pruned stubs of 1004, especially, showed collars 
id' dead bark often two or three inches in width. Instead of 
forming a callous and healing over the wound, as would nor- 
mally occur, the tissue bad died and shriveled up but still clung 
to the stub. Tn most cases the bacteria which had caused the 
death of the bark bad died out the first season. In a few in- 
stances, however, the canker was observed to be active early in 
tin 1 spring, extending down the side of the adjoining limb. Two 



The Blight Canker of Apple Trees 



15 



badly diseased trees on this side of the orchard seem to have 
been the source of infection. Owing to their diseased condition 
they had been severely pruned the previous season and very 
probably the knife or saw had carried the bacteria to the 
healthy trees. Flies which were observed to constantly follow 
the pruner to suck up exuding sap may have been the direct 
agents in many cases in transferring the bacteria. The knife 
itself may convey the disease, as is shown by the following in- 




Fig. 13 — Body canker cleaned out, treated and painted about 
eight weeks after treatment. Good healthy calluses formed, 
which with proper care will completely heal this wound. 

eident: While making inoculations into the body of an apple 
tree on the station grounds, I had occasion t < > remove from near 
the base a large sprout of several years' growth. This I did 
with my knife which 1 had but shortly before used to cut bark 
from a fresh canker. A typical canker soon developed about 
this pruned stub. 

Of a similar nature are infections that occur through wounds 
or bruises on the limbs <ui<l bodies of trees. These wounds, 



16 Wisconsin State Horticultural Society 

commonly known as "barking-," may be made by careless work- 
men when plowing or working about the trees or from the 
gnawing of animals, one of the worst of which in New York is 
the woodclmck. A large per cent of such wounds heal over 
eventually, but frequently through the agency of insects or 
oilier other means these wounds serve as infection courts for the 
canker bacillus. An interesting case of wound infection came 
under my observation this season. In cutting a cankered branch 
from a tree I accidently "barked" a healthy limb with the cut 
end of the diseased branch. The tree was not again visited 
until seme weeks later, when a large and actively spreading 
canker was found to have developed about the abrasion. The 
bacteria were f< und in abundance in the diseased tissue and 
pine cultures obtained. 

The iron ads or punctures of insects seem to be directly re- 
sponsible for some of the infections. Occasionally cankers on 
the bodies of trees cannot be attributed to infection through 
blighted shoots. In some cases these cankers have been traced 
directly to the wounds made by insects. It is probable that 
many of the cankers at the base of young trees originated in 
wounds made by borers. One und< ubted case of this kind came 
under my observation last summer. The bacteria are probably 
canied to these wounds by flies or other insects which visit these 
places to feed on the exuding sap and excrement. The infect- 
ing agents in the case of crotch cankers have not as yet been 
definitely located. It seems likely that insects are here again 
responsible. 

I have found them repeatedly hiding in the crevices of the 
dead bark that accumulates in the crotches, and one species 
seems to feed to some extent on the living tissues in such places. 
I have also observed this same species feeding on the exuding 
sap of cankered Limbs and stubs. That it may carry the bac- 
teria to the crotches seems obvious. Besides this many of the 
crotches are of such a form that they readily retain moisture 
and thus afford the besl of conditions for bacterial growth. 

As a general deduction, then, it may be stated that infection 
occurs only through a wound of some sort. Moreover, the in- 



The Blight C anker of Apple Trees 



17 



fection court must be of such a nature that it will not dry out 
quickly. An abundance of moisture is known to be necessary 
to the rapid growth and development of the blight organism. 
This peculiarity accounts for the ease with which growing shoots 




PlG. 14— Crotch cankers, Wausau Orchard. Treated 
July, 1906, but work not thoroughly done. Note the can- 
ker extending on central branch. The branch on right i-~ 
also affected for several inches. Photo, July 1907. 



are affected. Where the diseased tissue of an active canker was 
at once cut out and the wound exposed to the drying heat of 
the sun without any other treatment, the canker ceased to 
spread and the place healed rapidly. 



18 Wisconsin State Horticultural Society 

TREATMENT THAT PROMISES BEST RESULTS. 

Although the work of the past season has heen devoted largely 
to a study of the various manifestations of the disease, its cause 
and distribution, still some attention has been given to the 
means of combating it! Prevention rather than cure is one of 
the axioms of plant pathology. In most cases the curing of a 
diseased pbmt is impossible or its value does not warrant the 
effort required to save it. However, in the case of trees just 
coming into bearing it seemed that if possible some means of 
saving them should be worked out. Several things were ac- 
cordingly tried, but the one that so far gives most promise of 
definite results is to cut out the cankers. With a sharp knife re- 
move all the diseased tissue, swab out the wound with a solu- 
tion of corrosive sublimate (one tablet to cue pint of water) or 
with a solution of copper sulphate, 1 oz. to 2 gallons water, and 
when dry paint over thoroughly with some heavy lead paint. 
This should be d< ne early in the season as soon as the cankers 
are discovered, for two reasons: 1st, the spreading ef the can- 
ker and its consequent damage to the tree is stopped; and 2nd, 
the wound is thus given a long period in which to heal. The 
painting should be repeated again toward the close of the sea- 
son and again the next year or until the wound has completely 
healed. This prevents a second infection or the entrance of rot 
fungi. A bi-monthly inspection of every tree should be made 
and all cankers carefully cut out and treated as soon as they 
appear. Cankered trees so treated early in the spring of 1905 
have formed good calluses and are fast healing the wounds. 

PREVENTIVE MEASURES. 

It is scarcely necessary to point out that every precaution 
should be taken to prevent bruises or injuries of every sort, 
since these make excellent infection courts for the entrance of 
the bacteria. 

All dead limbs and trees should be promptly removed from 
the orchard and burned. Old pear trees in the neighborhood of 
young apple orchards are often a constant source of infection 



The Blight Canker of Apple Trees 



19 



and unless kept absolutely free of the blighl should be removed. 
A neighbor careless in respecl to blight in his pear trees is a 
dangerous one. 

Cut out and burn every trace of twig blight from both pear 

and apple trees as soon as it is detected. 



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Fig. 15 — Crotch canker, Wausau Orchard. Treated July 
1906; photo, July 1907. Treatment thorough and effective. 
Canker completely checked and tree saved. 

"When pruning, treat all cut surfaces with the corrosive sub- 
limate or copper sulphate solution and keep them painted until 
healed. Treat all accidental wounds in the same way. 

Keep the body and main limbs of the tree free of water- 
sprouts throughout the summer. 

In planting, select trees with open or spreading crotches. 



20 



Wisconsin State Horticultural Society 



Avoid excessive fertilizing with nitrogenous manures. Apply 
some form of phosphoric acid to ripen new growths. 

The planting of varieties known to be more or less resistant 
to this disease is to be recommended. The Wolf River and 




Fig. 16— Results of timely and thorough treatment. 
Similar to Fig. 15. 

Talman Sweet appear to be of this sort, while Baldwins and 
Ben Davis suffer most severely. Desirable non-resistant varie- 
ties may be top grafted on to resistant stocks. 

CONCLUSIONS. 

Injuries caused by blight canker are often ascribed to "sun- 
scald" and "winter-killing." 

Blight canker is most often found on young trees, 8 to 15 
years old. 



The Blight Canker of Apple Trees 21 

Indicated, in most cases, by discolored and distinctly sunken 
areas of bark. 

"When active, cankers exude sticky fluid on warm and cloudy 
days. 

Vary in size from one-half inch in diameter to a foot or more 
in length. 

Frequently found in crotches. 

Cuts off food supply; girdles branch or trunk. 

Caused by same organism that causes tire blight of pear and 
twig blight of apple. 

Trunks and crotches may be infected from : watersprouts, 
pruning knife; punctures of insects; "barking." 

Treatment.— Cut out all cankered tissues, disinfect with cor- 
rosive sublimate or copper sulfate and cover wounds with paint. 



Addenda 

P. CRANEPIELD. 

In the spring of 1906 treatement was begun of the affected 
trees in the Wausau orchard. 

It was found that about 100 of the trees were too far gone 
to warrant treatment and these were removed and the remainder 
treated as recommended in this bulletin. All cankers discov- 
ered were cut out, the wounds scraped clean, disinfected and 
painted. Pruning knives and gouge chisels were used. 

The expense for labor and material was a little over forty 
dollars. 

Over 90 per cent of the affected trees recovered and the en- 
tire appearance of the orchard was changed. A few of the trees 
were so badly affected, over one-half of the circumference of 
the bark on the trunks being removed, that recovery was de- 
layed. Some of these died the following season and others are 
slowly recovering. 

Had every canker in the orchard been found and treated the 
disease would have been completely eradicated, for a time a1 
least. Naturally, however, some escaped treatment and in oth- 



The Blight Canker of Apple Trees 23 

ers the cutting was not severe enough, a little of the affected 
bark being left to extend the canker. A case of this kind is 
shown in Fig. — . 

When the treatment was thorough the wound began to heal 
at once, the new bark completely closing the smaller wounds by 
the end of the season. This caution .should then be repeated; 
cut out all of the diseased tissues. Do not fail to cut to the 
live cambium, as the wound will soon heal if all of the canker 
is removed. 

The orchard was gone over carefully later in the season and 
again in the spring of 1907. On the whole the effect of the 
treatment was remarkable and the orchard probably saved from 
destruction, for it is but reasonable to assume from the general 
appearance as a whole and the rapid progress of the disease in 
1905 that two or three years more would have sufficed to kill 
mcst of the trees. 

Observations in 1907 showed plainly that the work must be 
kept up every season, as many new crotch and pit cankers were 
found on trees treated in 1906. 

The kinds most affected in the Wausau orchard are: North- 
western Greening, Longfield, Wealthy, Duchess, Peerless, New- 
ell, "Repka. and Hoadley, about in the order named. 

The following were but little affected: McMahon, Patten 
Greening, Malinda, Wolf River, Okabena, and Dominion 
Winter. 

Not a single canker was found on any of the 38 Hibernal 
trees. 

The lesson in this orchard has been somewhat expensive in 
lass of trees, etc.. but may prove very valuable if it results in 
calling the attention of even a small portion of those who have 
young apple trees to this most insidious and dangerous of or- 
chard diseases. 



LIBRARY OF CONGRESS 



002 811 193 9 • 



